Device for removably securing a tool to a machine spindle

ABSTRACT

The invention relates to a device for removably securing a tool (12) to the spindle (10) of a machine tool with a fitting aperture (16) concentric with the spindle axis, a fitting pin (18) engaging in the fitting aperture (16), two clamping bolts (26) arranged in the fitting pin so as to be radially movable towards opposite sides, a clamping member (32) movable axially by means of a tensioning mechanism fitted on the spindle side and two tapered surfaces (48, 30) fitted on the clamping member (32) on the one hand and on the clamping bolts on the other for the radial adjustment of the clamping bolts (26) between a release position withdrawn in the fitting pin (18) and a clamping position shifted radially outwards. In order to be able to clamp large tools securely, even with a relatively short axial clamping travel of the central securing and clamping mechanism on the spindle side, the clamping member (32) and the clamping bolts (26) each have a transverse groove therein (50, 52) limited by transverse sides in the region of their facing tapered surfaces (48, 30) by means of which the tapered surfaces are divided into two partial surfaces arranged at a distance from each other. In the release position, one of the partial surfaces (48&#34;, 30&#39;) is received in the opposite transverse groove (50, 52) in the manner of a toothed gear, while in the clamping position both partial surfaces (30&#39;, 48&#39;, 30&#34;, 48&#34;) lie mutually opposite each other.

FIELD OF THE INVENTION

The invention relates to a device for releasably connecting a tool to aspindle of a machine tool comprising a fitting aperture concentric withrespect to the spindle axis, a fitting pin extending into the fittingaperture, at least one clamping bolt movably supported in radialdirection in the fitting pin, a clamping member axially movable by meansof a clamping mechanism arranged in the spindle, and two taperedsurfaces, one being provided on the clamping member and the other beingprovided on the clamping bolt, are positioned inclined with respect tothe spindle axis, and rest against one another for facilitating a radialadjustment of the clamping bolt between a release position pulled backinto the fitting pin and a radially outwardly extended clampingposition.

BACKGROUND OF THE INVENTION

Connecting devices of this type are primarily used in machine toolshaving an automatic tool exchange in particular for machining centerswith a center tool-feeding apparatus. This tool-feeding apparatus, whichis primarily provided with a steep-angle taper to receive the tool,operates in most machining centers through a cup-spring package withhydraulic relaxation. A head bolt arranged on the steep-angle taper ispulled into the spindle by a tong-like gripping means clamping thesteep-angle taper. The clamping path needed in the case of thesteep-angle taper amounts to approximately 6 to 10 mm depending on thesize of the spindle. In order to achieve at a given spindle size anincreased support compared with the steep-angle taper connection, it hasalready been suggested to replace the steep-angle taper receiving meanswith a cylindrical receiving means having a front-face planar surfacesupport for the tool (Magazine "Werkstatt und Betrieb" 119 (1986), Pages797 to 801) and to use at the same time the center tool-feedingapparatus already existing in many machine tools as a clampingmechanism.

Thus, the conventional tool of the type mentioned above has two clampingbolts radially movably supported in the fitting pin, which clampingbolts can be moved diametrically outwardly by a clamping member designedas a drawing part and axially movable by the clamping mechanism arrangedon the spindle. In their outwardly moved clamping position, the clampingbolts, with their truncated-cone-shaped tips, extend into a conicalrecess in the area of the bore wall of the receiving means in order topull an annular planar surface adjoining the fitting pin against aplanar surface adjoining the fitting aperture and to brace same. Theclamping bolts were in the release position pulled so far back into thefitting pin that the fitting pin can be pulled out of the fittingaperture during the tool exchange. The clamping force transferable ontothe tool coupling at a given feeding force provided by the centerclamping mechanism is larger the smaller is the wedge angle of the wedgedrive formed by the tapered surfaces of the clamping member and of theclamping bolt. On the other hand, it is not possible to reduce at randomthe size of the wedge angle of the known tool coupling since thiseffects also the radial stroke of the clamping bolts as a given axialadjustment path of the clamping mechanism becomes smaller. Thisdisadvantage exists in particular in the case of larger tools, whichbesides an increased clamping force require also a greater adjustingstroke of the clamping bolt. Thus, the known clamping mechanisms withcup-spring packages cannot easily be utilized mainly in larger toolswith planar-surface bracing. Instead, hydraulic tool-clamping means havealready been utilized, which enable a larger adjustment path. The hereneeded, complicated change-over of machine tools and machining centerslimits, however, the area of use of the tools with planar-surfacebracing.

SUMMARY OF THE INVENTION

The basic purpose of the invention is therefore to provide a connectingdevice of the above-mentioned type, which also in the case of largetools guarantees a reliable planar-surface bracing with a high clampingforce and which is still sufficient with a relatively small axialclamping path provided by the center pull-in and clamping mechanism onthe spindle.

The invention is mainly based on the thinking that the major portion ofthe stroke path is necessary for the almost force-free movement of theclamping bolt from its release position, in which it is pulled back intothe fitting pin, into its clamping position, and that the actualclamping operation requires only a very small stroke path. In order toguarantee, on the other hand, a moment-free transfer of force, it mustbe assured that the tapered surfaces rest on one another and have alarge base surface during the actual clamping operation. In order toachieve this, the invention suggests that the clamping member and theclamping bolt have a transverse groove defined by transverse flanks inthe area of their tapered surfaces facing one another, through whichtransverse groove the tapered surfaces are each divided into two partialsurfaces arranged spaced from one another, and limited on one side byone of the transverse flanks and on another side by an outer transverseedge, that in the release position each of the partial surfaces extendsinto the oppositely lying transverse groove in the manner of a toothedgear, that during the clamping operation at least one of the transverseflanks and/or transverse edges which strike one another has a receivingslope which is steeper relative to the spindle axis compared with thetapered surface, and that in the clamping position both partial surfacesrest against one another.

An optimum adjustment to the given clamping mechanism can be achievedalso for large tools because the taper is adjusted to a range of from 8°to 20° and the receiving slope to a range of from 40° to 70°.

The transverse grooves in the clamping bolt and in the clamping memberhave in the finished state an essentially trapezoidal cross section withoutwardly diverging flanks. According to an advantageous development ofthe invention, the receiving slope has an angle variable with respect tothe spindle axis. It can, for example, be curved convexly and, ifnecessary, transfer continually and smoothly into the tapered surface.

In order to keep the maximum torque transmitted during the clampingoperation by the clamping member onto the clamping bolt as small aspossible, the transverse flank of the clamping bolt is rotationallysymmetrical on its outer surface, which transverse flank hits during theclamping operation the clamping member first near the axis of theclamping bolt. The transverse edge of the clamping bolt, whichtransverse edge hits the transverse flank of the clamping member duringthe clamping operation, is at least once, preferably twice chamfered orconvexly curved.

According to a preferred development of the device of the invention, inwhich the clamping bolt has two guide cheeks for the clamping member,which guide cheeks laterally limit the tapered surfaces, the transversegroove of the clamping bolt is limited at least at one end by one of theguide cheeks.

When the transverse groove is manufactured using the spark-erosionmethod, the front-face boundary surfaces of the transverse grooveproject step-like over the guide surfaces of the guide cheeks, while theclamping member has at its lateral guide surfaces in the area of theparts engaging the transverse groove a corresponding material removal.

When on the other hand the transverse groove is a milled groove, thenthe milling tool can be introduced through a premanufactured slottedhole in one of the guide cheeks, while on the side opposite the slottedhole and in extension of the transverse groove a blind hole with thecontour of the transverse edge can be formed from the inside into therespective guide cheek. A material removal on the clamping member is notnecessary in this case.

In order to guarantee a sufficient lubrication in the area of thetapered surfaces, the clamping bolt has a lubricating channel leadingfrom its preferably cylindrical outer surface to the tapered surface,with one end of the lubricating channel terminating in the transversegroove.

The lubrication is preferably done through transverse bores, whichextend through the guide cheeks into the transverse groove. A transversebore is advantageously arranged in each guide cheek, with the transversebores being able to extend into the transverse groove preferably in thearea of each one of the transverse edges, a blind hole open toward thetransverse groove and aligned with the transverse bore being able to bearranged in the respectively oppositely lying guide cheek. At least oneof the transverse flanks can thereby be formed by a portion of thetransverse-bore surface, which portion extends into the area of thetapered surface. The latter is the case when the transverse bores areused at the same time as auxiliary bores during the manufacture of thetransverse groove using the milling method. The transverse-groove basecan then be aligned essentially perpendicularly with respect to thetransverse-bore axis. A centering bore can be introduced as amanufacturing aid into the transverse-groove floor, which centering boreis coaxial with respect to the clamping-bolt axis and, if necessary,intersects the receiving slope.

The clamping bolt is during a tool exchange, when the clamping mechanismis released, moved automatically into its release position within thefitting pin through engagement of the conical tip with the spindle bore.Since during the removal task the tool is slowly accelerated by the toolchanger, the force peaks hereby acting onto the clamping bolt arerelatively small so that a forced movement of the clamping bolt by theclamping mechanism is not problematic. This thinking does notnecessarily apply to the equipping operation since there the fitting pinis moved with a relatively high speed into the fitting aperture andaccordingly a projecting clamping bolt will be loaded with a high peakforce. According to a preferred further development of the invention, itis therefore suggested that the clamping bolt be releasably held in arelease pulled back position in the in the fitting pin. This can beaccomplished by a device having a stop screw screwed into a fitting pinand extending with its tip into a groove of the clamping bolt, whichgroove is closed as its ends, by the screw tip carrying a locking ballmovable against the force of a spring, which locking ball engages in thepulled-back release position of the clamping bolt a locking recessarranged in the area of the floor of the groove. The locking connectionbetween the clamping bolt and the fitting pin created in this mannerduring a tool exchange is again released without a great input of forcebeing required during the clamping operation by the clamping mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be discussed hereinafter in greater detail inconnection with one exemplary embodiment schematically illustrated inthe drawings, in which:

FIG. 1a is a cross-sectional view of a connecting device between amachine spindle and a tool in the clamping position;

FIG. 1b is a cross-sectional view of the connecting device in therelease position;

FIG. 1c shows a detail enlargement of FIG. 1a;

FIG. 2 is a cross-sectional view of a locking mechanism for the clampingbolt;

FIG. 3 is a perspective illustration of a clamping bolt with a milledtransverse groove;

FIG. 4 is a perspective illustration of a further exemplary embodimentof a clamping bolt with a milled transverse groove;

FIG. 5 is a partially cross-sectioned top view of the clamping boltaccording to FIG. 4;

FIG. 6 is a cross-sectional view taken along the line of intersection6--6 of FIG. 5;

FIG. 7 is a perspective illustration of a further exemplary embodimentof a clamping bolt with a milled transverse groove and an erodedreceiving slope;

FIG. 8 is a top view of the clamping bolt according to FIG. 7;

FIG. 9 is a cross-sectional view taken along the line of intersection9--9 of FIG. 8.

DETAILED DESCRIPTION

FIGS. 1a and b show that a tool 12, for example a boring rod (nototherwise illustrated), can be replaceably connected by means of aconnecting device 14 to a rotatably supported spindle 10 of a machinetool (not otherwise illustrated), for example of a machining center. Thespindle 10 has for this purpose a fitting aperture 16 which isconcentric to the spindle axis and into which can be axially guided acylindrical fitting pin 18 arranged on the tool. In the tensioned stateof the connecting device, the annular planar surface 20, defining thefront face of the fitting aperture 16 and the planar surface 22annularly surrounding the fitting pin at its root are axially pressedagainst one another. This planar surface bracing is achieved by thehereinafter described coupling mechanism:

Two diametrically opposite clamping bolts 26 are radially movablysupported in a radial bore 24 in the fitting pin 18. The clamping bolts26 each have an essentially cylindrical outer surface 27, a radiallyoutwardly extending truncated-cone-shaped tip 28 and an inwardlyextending tapered surface 30. Between the tapered surfaces 30 of the twoclamping bolts 26, which tapered surfaces face one another, there isprovided a clamping member 32, which is designed as a double taperedwedge-shaped member and which is rigidly connected to a pull rod 34axially projecting beyond the free end of the fitting pin 18 and isaxially movable relative to the fitting pin. The pull rod 34 carries acoupling element 36 which can be clamp-like enclosed by a clampingmechanism on the spindle, which clamping mechanism is not illustrated inthe drawings. A cavity 38 for receiving the clamping member 32 in therelease position is arranged in the tool body 12. Screw threaded plugs42 are screwed into the spindle 10 in the area of the fitting aperture16 in two diametrically opposed internally threaded openings 40, whichscrew plugs have radially inwardly extending conical recesses 44 forreceiving the truncated-cone-shaped tip 28 of the respectively adjacentclamping bolt 26. When the pull rod 34 is axially moved in direction ofthe arrow 46 by the clamping mechanism (not illustrated), then thismovement is converted into a radial stroke of the clamping bolts 26through the wedge-shaped clamping member 32. The truncated-cone-shapedtips 28 penetrate thereby into the conical recesses 44 in the screwplugs 42 until a bracing of the conical and tapered surfaces, which restagainst one another and, as a consequence of the relative axial shiftingof the mentioned surfaces, a bracing of the planar surfaces 20, 22occurs.

The clamping member 32 and the clamping bolts 26 each have in the areaof their opposing tapered surfaces 48 or 30 one transverse groove 50, 52defined by transversely extending flanks 50', 50" or 52', 52", whichtransverse grooves divide each of the tapered surfaces 30 or 48 into twopartial surfaces 30', 30" or 48', 48" arranged spaced from one another,and limited on the one side by one of the transverse flanks and on theother side by an outer transverse edge 26', 26" or 32', 32". In therelease position (FIG. 1b), each of the partial surfaces 30' or 48" isreceived in the oppositely lying transverse groove 52 or 50, while inthe clamping position (FIGS. 1a, c), both partial surfaces 30', 48' or30", 48" rest in pairs against one another. The transverse flanks 52' ofthe transverse groove 52 and the transverse edges 32' of the clampingmember 32 strike in pairs against one another during the clampingoperation. The edges are on the rod side and form a receiving slopewhich is steeper compared with the tapered surface 30 or 48 relative tothe spindle axis, so that in the transition area the axial path ofmovement of the pull rod 34 is converted into a relatively large strokeof the clamping bolts 26. This is possible because the stroke conversionoccurs practically force-free. The actual clamping operation starts onlywhen the tapered surfaces 30' or 48' on the one side and 30" or 48" onthe other side are moved with their small tapered angle against oneanother and thereby guarantee a correspondingly large power ratio. Thebase surface of the wedge drive is not changed in the clamping state bythe transverse grooves 50 and 52. The gap in the tapered surface createdby the transverse grooves is even of an advantage during the clampingoperation, if one considers the machining inexactnesses during themanufacture of the planar surfaces.

In order to prevent an inadvertent removal of the clamping bolts 26 fromthe fitting pin 18, the stroke of the clamping bolts 26 is limited inboth directions by a longitudinal groove 60 (FIG. 2) closed at its endsand a stop screw 62 screwed into the fitting pin 18 so that its tip 64extends into the longitudinal groove 60. The stop screw 62 has in itsshaft a cylindrical bore 66 open toward the tip. A compression spring 68and a locking ball 70 are arranged in the bore 66. The locking ball 70,when the clamping bolt 26 is in its released pulled back position intothe inside of the fitting pin 18, extends into a locking recess 72arranged in the base of the groove so that the clamping bolt, during ahandling of the tool 12 outside of the machine spindle 10, cannot reachits outwardly shifted position. The locking connection is released onlywhen the clamping operation is started by reason of a tool having beenplaced onto the spindle 10.

The tapered surface 30 of each clamping bolt is positioned laterallybetween guide cheeks 74 for guiding the clamping member 32 therebetween.A cylindrical notch 76 assures that the pull rod 34 in the releaseposition can still extend past the clamping bolt when the clamping boltis pulled back into the fitting pin.

The transverse groove 52 in the clamping bolt illustrated in FIG. 3 ismanufactured by a milling method. One of the side cheeks 74 is, for thispurpose, first provided with a slotted hole 80 through which the millingtool can be introduced from the side into the area of the taperedsurface 30. The slotted hole 80 is changed during the milling operationto the trapezoidal contour of the transverse groove 52. A blind-holelikerecess 82 with the same contour as the transverse groove 52 is milledalso during the milling operation into the side cheek opposite theslotted hole 80. The recess 82 guarantees that a removal of materialfrom the side cheek of the clamping member 32 is not necessary.

Lubricant bores 84, 86 leading from the outer surface 27 to the taperedsurface are furthermore provided in the clamping bolt 26, the end 88 ofwhich bores terminating within the transverse groove 52.

FIGS. 4 to 6 show a further exemplary embodiment of a clamping bolt 26,which embodiment is modified compared with FIG. 3. The transverse grooveof the clamping bolt is manufactured by a milling method. Two transverseblind bores 90, 92, which are arranged offset from one another, arefirst machined from opposite sides into the rod-like blank.Subsequently, when the tapered surface 30 between the two side cheeks 74is milled into the blank, the bore 90 breaks open toward the slopedsurface. It is then possible to begin machining through the broken openbore 90 the transverse groove 52 with a cutter introduced at the frontface into the space between the guide cheeks 74 and to break into thetransverse bore 92, with the remaining wall part 90' forming thetransverse flank 52' of the transverse groove 52. The transverse flank52" receives a vertical section 93 during the milling operation, whichsection is chamfered toward the tapered surface 30 forming the receivingslope. A coaxial centering bore 96 is formed as a manufacturing aid intothe floor 94 of the transverse groove 52, which floor is perpendicularwith respect to the axis of the bolt. The centering bore 96 intersectswith its edge area into the transverse flank 52'. The edge steps 98remaining after the milling operation in the area of the receiving slope52' must take into consideration a suitable material removal on thewedge-shaped member 32 so that the two parts can mate in the area oftheir respective transverse grooves. The through bore sections 90, 92remaining in the side cheeks 74 form in the finished clamping bolt alubricant bore leading from the outer surface 27 to the tapered surface30. The furthermore remaining blind holes 90", 92" have only a smalldepth of approximately 0.1 mm and guarantee that at this point duringthe machining operation no material projection remains toward the insideof the guide cheeks 74.

In the exemplary embodiment of a clamping bolt 26 illustrated in FIGS. 7to 9, the deep part of the transverse groove 52 between the side cheeks74 is manufacture by a milling method after the tapered surface 30 hasfirst been milled. The transverse flank 52' receives during the millingoperation a vertical section 93, which is subsequently chamfered by aneroding method forming thereby a receiving slope toward the taperedsurface 30. The receiving slope extends in all areas to the side cheeks74 so that the corner radii with the edge steps 98 occurring in theexemplary embodiment according to FIGS. 4 to 6 are eliminated.Furthermore, by using this method of manufacture, the transverse bores90, 92 or openings 80 in the side cheeks are not needed.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. In a device forreleasably connecting a tool to a spindle of a machine tool comprising afitting aperture concentric with respect to the spindle axis, a fittingpin extending into the fitting aperture, at least one clamping boltmovably supported in radial direction in the fitting pin, a clampingmember axially movable by means of a clamping mechanism arranged in thespindle, and two tapered surfaces, one being provided on the clampingmember and the other being provided on the clamping bolt, are positionedinclined with respect to the spindle axis, and rest against one another,for facilitating a radial adjustment of the clamping bolt between arelease position pulled back into the fitting pin and a radiallyoutwardly extended clamping position, the improvement wherein theclamping member and the clamping bolt each have a transverse groovewhich face one another defined by transverse flanks in the area of theirrespective tapered surfaces, through which transverse groove the taperedsurfaces are divided into two partial surfaces each lying in the sameplane arranged spaced from one another and limited on one side by one ofthe transverse flanks and on another side by an outer transverse edge,wherein in the release position, each of the partial surfaces extendsinto the oppositely lying transverse groove, wherein, during theclamping operation, at least one of the transverse flanks and/ortransverse edges that strike one another has a receiving slope which issteeper relative to the spindle axis compared with the tapered surface,and wherein in the clamping position both partial surfaces rest againstone another.
 2. The device according to claim 1, wherein the receivingslope has a pitch that varies with respect to the spindle axis.
 3. Thedevice according to claim 1, wherein at least one of the receivingslopes is curved convexly.
 4. The device according to claim 3, whereinat least one of the receiving slopes transfers smoothly into the taperedsurface.
 5. The device according to claim 1, wherein the transverseflank of the essentially rotationally symmetrical clamping bolt, whichtransverse flank during the clamping operation first strikes theclamping member, is arranged near the axis of the clamping bolt.
 6. Thedevice according to claim 1, wherein the transverse edge of the clampingbolt, which transverse edge strikes the transverse flank of the clampingmember during the clamping operation, is at least once chamfered orconvexly curved.
 7. The device according to claim 1, in which theclamping bolt has two guide cheeks for the clamping member, which guidecheeks laterally limit the tapered flanks, wherein the transverse grooveof the clamping bolt is limited at least at its one end by one of theguide cheeks.
 8. The device according to claim 1, wherein the transversegroove of the clamping bolt is manufactured or milled by thespark-erosion method.
 9. The device according to claim 8, whereinfront-face boundary surfaces of the transverse groove project step-likeover the guide surfaces of the guide cheeks, and wherein the clampingmember has at its lateral guide surfaces in the area of the partsengaging the transverse groove a corresponding material removal.
 10. Thedevice according to claim 1, wherein the transverse groove of theclamping bolt is milled and the transverse flank striking the clampingmember is eroded in the area of the receiving slope.
 11. The deviceaccording to claim 8, including a through slotted hole arranged inextension of the transverse groove in one of the guide cheeks.
 12. Thedevice according to claim 11, including a blind hole arranged inextension of the transverse groove in one of the guide cheeks.
 13. Thedevice according to claim 1, wherein the transverse grooves have anessentially trapezoidal cross section with at least one outwardlydiverging flank.
 14. The device according to claim 1, wherein theclamping bolt has a lubricating channel leading from its cylindricalouter surface to the tapered surface, with one end of the lubricatingchannel terminating at the transverse groove.
 15. The device accordingto claim 1, wherein the clamping bolt is releasably lockable in itsrelease pulled back position into the fitting pin.
 16. The deviceaccording to claim 15 including a stop screw screwed into the fittingpin, a tip of the screw being received in a boundary groove closed atits end, wherein the screw tip carries a locking ball movable againstthe force of a spring, which locking ball, in the pulled back releaseposition of the clamping bolt, extends into a locking recess arranged inthe area of the floor of the groove.
 17. The device according to claim1, wherein the tapered surface defines an angle of 8° to 20° with thespindle axis.
 18. The device according to claim 1, wherein the receivingthe slope defines an angle of 40° to 70° with the spindle axis.
 19. Thedevice according to claim 1, including at least one transverse boreending through one of the guide cheeks in the transverse groove.
 20. Thedevice according to claim 19, wherein in each guide cheek there isarranged a transverse bore ending in the transverse groove.
 21. Thedevice according to claim 20, wherein the transverse bores end in thearea of each one of the transverse edges in the transverse groove. 22.The device according to claim 19, including a blind hole aligned withthe transverse bore and open toward the transverse groove in theoppositely lying guide cheek.
 23. The device according to claim 19,wherein at least one of the transverse flanks is defined by a part ofthe transverse bore surface, which part extends into the area of thetapered surface.
 24. The device according to claim 1, wherein thereceiving slope is constructed as a chamfer in a transverse flankessentially parallel with respect to the clamping bolt axis.
 25. Thedevice according to claim 1, wherein the transverse groove floor isaligned essentially perpendicular with respect to the clamping boltaxis.
 26. The device according to claim 1, including a centering bore inthe transverse groove floor, which centering bore is coaxial withrespect to the clamping bolt axis.
 27. The device according to claim 1,wherein the receiving slope is intersected by the centering bore.